Conventionally, active energy beam-curable inks for inkjet printing have been supplied to, and used in offset printing, silk screen printing, and as top coat materials. In recent years, the quantity used of active energy beam-curable inks used has continued to increase, as such inks enable a simplified drying process and reduced costs, and also offer the environmental advantage of enabling a reduction in the volume of volatilized solvents.
Currently, both water-based inks and solvent-based inks are widely used as inkjet inks. These inkjet inks are used in different situations in accordance with their respective features, but their use in industrial applications faces a variety of problems, including restrictions on the printing substrate, a comparatively poor level of water resistance, a large quantity of energy required for drying the ink, and adhesion of ink components to the printing head if the ink volatilizes within the head. Accordingly, the replacement of such inks with active energy beam-curable inks, which can be used with all manner of printing substrates, exhibit favorable water resistance, require no heat energy for drying, and exhibit comparatively low levels of volatility, has been keenly anticipated.
However, although cured films formed using conventional active energy beam-curable inks are hard, they are often brittle. Furthermore, because the cured films of active energy beam-curable inks exhibit significantly inferior stretching processing properties to conventional solvent-based inks, active energy beam-curable inks tend to be unsuitable for high quality printing applications that require forming processing.
The following types of inks have been proposed in order to address the types of problems described above. Japanese Patent Laid-Open No. H05-214280 discloses an ink comprising a colorant and from 50 to 95% by weight of polymerizable monomers, wherein the ink comprises a maximum of 70% by weight of monofunctional monomers, a maximum of 70% by weight of bifunctional monomers, and from 0 to 10% by weight of trifunctional or higher monomers.
Japanese translation of PCT international application No. 2004-514014 discloses an ink composition comprising a heterocyclic radiation curable monomer and/or an alkoxylated monomer that comprise pendant alkoxylated functionality.
In order to alleviate shrinkage upon curing, Japanese translation of PCT international application No. 2004-518787 discloses an ink composition comprising an oligomer that is a reaction product of an aliphatic polyisocyanate and a radiation curable alcohol that comprises one or more radiation curable moieties, one or more hydroxyl moieties and one or more polycaprolactone ester moieties, and a reactive diluent.
Japanese Patent Laid-Open No. H06-184484 discloses an ink composition comprising a polycaprolactone-based urethane acrylate oligomer, a vinylcaprolactam and a phenoxy acrylate.